1. Field of the Invention
The present invention is generally directed to a method and apparatus for the fine adjustment of a potentiometer, and particularly, a method and apparatus which is adapted for use with an already-existing display unit, for example, a display unit in an appliance, to indicate when the proper adjustment of the potentiometer has been made, and to provide such an adjustment without the use of external meters.
2. Description of the Prior Art
A wide variety of appliances, commercial and domestic, have potentiometers located in their circuitry that require adjustment. FIG. 4 illustrates such a circuit 22 from a dryer apparatus containing potentiometer 70. Potentiometers can be located in many different circuit layouts and in no way is the invention limited to the circuit 22 illustrated in FIG. 4.
The method of adjustment according to the prior system consists of substituting a high precision resistor in place of the thermistor. Attachment of an external frequency meter reads the output frequency from operational amplifier 68. Potentiometer 70 was then adjusted by rotating its shaft, not shown, in the usual manner until the frequency meter displayed the desired frequency.
There arises the following problems with the prior systems. First, the external frequency meter causes a loading effect on circuit 22. This in and of itself causes a variation between the true frequency versus the measured frequency. In addition, different frequency meters have different loading effects on a circuit. This particularly creates difficulties when the meter used to manufacture and test the board on which the potentiometer resides is different from the meter used in inspecting and installing the board in the appliance or the meter used during maintenance or repair. Thus there is a lack of accuracy and difficulty in reaching repeatability standards using the prior art system. Finally, the frequency meter may have a slow readout response time. Thus in order to make a proper adjustment to the potentiometer, one must wait for the delay period before making further adjustments. If the adjustments are made too quickly, the proper setting will be overshot resulting in either a longer adjustment process or an inaccurate one.